Collecting carrot seeds is fairly easy. Producing them takes a lot of work. Carrots will not seed until their second year of growth, so they must be dug and kept over the winter, then replanted in order to flower and produce seeds for collection. It’s a 2-year effort, but can be accomplished by the intrepid gardener through careful cultivation and storage. Do not attempt to grow carrot seed if the original carrot is a hybrid variety, because hybrid seeds are not generally viable. Start from scratch with non-hybrid seeds if this is the case.
Put on garden gloves and dig up existing carrots with a spade in the fall, before the killing frost. Dig around the carrot top to a depth of 6 inches, loosening the soil while being careful not to scratch the carrot root. Pull the carrots out gently to avoid breaking them.
Place carrot roots in a container that is ventilated at the bottom for drainage, stacking them in layers of peat. Keep cool and moist, but not wet, throughout the winter. Rotate the layers once a month to keep them uniformly moist.
Replant the carrots, in spring after danger of frost is past, in an area of the garden where they will have full sun and at least 2 square feet of space, because the flower stalk will grow quite large.
Water and fertilise with 1/2 tsp of plant fertiliser mixed with a water can full of water once a month throughout the spring. Flower stalks will grow and bloom, and when the blooms fade, seedpods will form.
Keep an eye on the seedpods throughout the next month or so, and collect them when they become dry and brittle. Get them before they fall, to prevent birds and squirrels from plundering your harvest.
Take the pods indoors and leave them on a plate or saucer in open air to complete the drying process. Break open the pods and shake the seed into a vented plastic sandwich bag. Store in a cool, dry place for sowing the following spring.